Non-volatile memory

ABSTRACT

A non-volatile memory and a method of fabricating the same are described. First, a substrate is provided. Then, a plurality of stack structures is formed on the substrate. Each stack structure comprises, from bottom to top, a bottom dielectric layer, a charge trapping layer, a top dielectric layer, a control gate and a cap layer. Next, a plurality of spacers is formed on the sidewalls of the stack structures. Thereafter, a gate dielectric layer is formed over the substrate. A word line is formed between two neighboring stack structures. After that, the cap layers in the stack structures are removed. A source and a drain are formed in the substrate beside the stack structures adjacent to the sides of each word line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of an application Ser. No. 10/907,707,filed on Apr. 13, 2005, now pending. The entirety of the above-mentionedpatent application is hereby incorporated by reference herein and made apart of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a non-volatile memory and fabricatingmethod thereof. More particularly, the present invention relates to anon-volatile memory and fabricating method thereof that can improve theelectrical properties and the reliability of the memory device.

2. Description of the Related Art

At present, one of the most common types of non-volatile memory is anelectrically erasable programmable read-only-memory (EEPROM) called the‘flash memory’. Flash memory allows multiple data writing, reading anderasing operations. Furthermore, the stored data will be retained evenafter power to the device is removed. With these advantages, flashmemory has become one of the most widely adopted non-volatile memoriesfor personal computer and electronic equipment.

A typical flash memory has a floating gate and a control gate fabricatedusing doped polysilicon. In the process of programming data into a flashmemory cell, the electrons injected into the floating gate willdistribute evenly throughout the entire doped polysilicon floating gatelayer. However, if the tunneling oxide layer underneath the dopedpolysilicon floating gate has some defects, a leakage current may flowfrom the device and lead to a drop in the overall reliability of thedevice.

To resolve the aforementioned leakage problem in the flash memory, anon-volatile memory having a charge trapping layer instead of the dopedpolysilicon floating gate called asilicon-oxide-nitride-oxide-semiconductor (SONOS) has been developed.Because a SONOS memory has an oxide-nitride-oxide (ONO) compositedielectric layer structure, the nitride layer can serve as a trappinglayer for electrons. In general, programming can be achieved byinjecting channel hot electrons (CHE) from the bottom oxide layer of theoxide-nitride-oxide (ONO) composite dielectric layer structure.Conversely, to erase stored data within the memory device, tunnelingenhanced hot holes (TEHH) can be injected through the bottom oxide layerof the oxide-nitride-oxide (ONO) composite dielectric layer structure.Thus, the SONOS memory is one important type of device that can combatleakage problems. However, as the dimension of devices continues todecrease, errors resulting from charge migration in the charge trappinglayer inside the aforementioned SONOS memory occurs more frequently.

In recent years, a type of memory with charge trapping occurring in theoxide-nitride-oxide dielectric structure (shown in FIG. 1) on each sideof the gate has been developed. FIG. 1 is a schematic cross-sectionalview of a conventional non-volatile memory. As shown in FIG. 1, the wordline 120 of the silicon-oxide-nitride-oxide-semiconductor (SONOS) memoryis formed on a gate oxide layer 110 above the substrate 100. The controlgates 170 are formed on the sidewalls of the word line 120 and areshaped like a spacer. The word line 120 and the control gate 170 as wellas the control gate 170 and the substrate 100 are separated from eachother by an oxide-nitride-oxide (ONO) composite structure comprising abottom dielectric layer 140, a charge trapping layer 150 and adielectric cap layer 160. The source 180 and the drain 190 are formed inthe substrate 100 beside the control gate spacer 170 on each side of theword line 120.

In the process of programming the device, because the charges aretrapped inside the charge trapping layer 150 on each side of the wordline 120, charge migration problem due to device miniaturization can beavoided. However, electric charges trapped inside theoxide-nitride-oxide (ONO) structures on the sidewalls of the word linewithin the SONOS non-volatile memory are difficult to remove. Hence,charges will accumulate and ultimately will lead to device reliabilityproblems.

On the other hand, because the control gate is shaped like a spacer, thecontrol gate has an arc surface instead of a plane surface. In thesubsequent process of fabricating a contact, a good electricalconnection between the contact and the control gate spacer is difficult.

In addition, the etching back operation used in the process of formingthe control gate spacers may damage the oxide-nitride-oxide (ONO)structure. Therefore, a short circuit is easily formed when a silicidelayer is subsequently formed between the word line and the control gatespacers.

SUMMARY OF THE INVENTION

Accordingly, at least one objective of the present invention is toprovide a non-volatile memory for improving the reliability of a memorydevice.

At least a second objective of the present invention is to provide amethod of fabricating a non-volatile memory that can improve theelectrical properties of a memory device.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, theinvention provides a method of fabricating a non-volatile memory. First,a substrate is provided. Then, a plurality of stack structures is formedon the substrate. Each stack structure comprises, from bottom to top, abottom dielectric layer, a charge trapping layer, a top dielectriclayer, a control gate layer and a cap layer. Thereafter, a plurality ofspacers is formed on the sidewalls of the stack structures. A gatedielectric layer is formed over the substrate. Next, a word line isformed between two neighboring stack structures. After that, the caplayers in the stack structures are removed. A source and a drain areformed in the substrate beside the stack structures adjacent to thesides of each word line.

According to one preferred embodiment of the present invention, themethod of forming the spacers in the process of fabricating thenon-volatile memory includes forming a spacer material layer over thesubstrate to cover the stack structures. Thereafter, the spacer materiallayer is etched back to form the spacers on the sidewall of the stackstructures.

According to one preferred embodiment of the present invention, themethod of forming the gate dielectric layer in the process offabricating the non-volatile memory includes performing a thermaloxidation process.

According to one preferred embodiment of the present invention, themethod of forming the word line between two neighboring stack structuresincludes forming a conductive layer over the substrate to cover thestack structures and fill the space between two neighboring stackstructures. Thereafter, a portion of the conductive layer is removed toexpose the cap layer of various stack structures. Than, a patternedphotoresist layer is formed over the substrate to cover the conductivelayer between two stack structures and expose at least a portion of thecap layer. After that, using the patterned photoresist layer as a mask,the cap layers of the stack structures are removed. Finally, thepatterned photoresist layer is removed.

According to one preferred embodiment of the present invention, themethod of removing a portion of the conductive layer to expose the caplayer of various stack structures includes performing achemical-mechanical polishing process using the cap layers of the stackstructures as a polishing stop layer.

According to one preferred embodiment of the present invention, themethod of removing a portion of the conductive layer to expose the caplayer of various stack structures includes performing an etching backoperation using the cap layer of various stack structures as an etchingstop layer.

According to one preferred embodiment of the present invention, themethod of removing the cap layer of various stack structures includesperforming a wet etching operation.

According to one preferred embodiment of the present invention, themethod of forming a source region and a drain region in the substrateincludes performing an ion implantation process.

The present invention also provides a non-volatile memory comprising asubstrate, a plurality of stack structures, a plurality of word lines, aplurality of spacers, a gate dielectric layer, a plurality of sourceregions and a plurality of drain regions. The stack structures aredisposed on the substrate. Each stack structure comprises a bottomdielectric layer, a charge trapping layer, a top dielectric layer and acontrol gate. In each stack structure, the bottom dielectric layer isdisposed on the substrate; the charge trapping layer is disposed on thebottom dielectric layer; the top dielectric layer is disposed on thecharge trapping layer and the control gate is disposed on the topdielectric layer. In addition, the word lines are disposed on thesubstrate between every pair of neighboring stack structures. Thespacers are disposed between the stack structures and theircorresponding word line. The gate dielectric layer is disposed betweenthe word line and the substrate. The source regions and the drainregions are disposed in the substrate beside the various stackstructures on each side of the word lines.

According to one preferred embodiment of the present invention, thecontrol gate of the non-volatile memory has a planar top surface.

In the non-volatile memory of the present invention, there is nooxide-nitride-oxide structure on the sidewalls of the word lines as inthe conventional silicon-oxide-nitride-oxide-semiconductor (SONOS)memory structure. Hence, there is no need to worry about chargestrapping in the oxide-nitride-oxide structure next to the sidewalls ofthe word line. In other words, overall reliability of the memory deviceis improved.

In addition, the control gate of the non-volatile memory of the presentinvention has a planar top surface. Therefore, it is much easier to forman electrical connection between the control gate and a contact in asubsequent contact fabrication process.

On the other hand, according to the method of fabricating thenon-volatile memory in the present invention, the formation of spacersbetween the word lines and the control gates is able to provide aneffective insulation that prevents any short-circuiting after asubsequent silicide fabrication process. Hence, electrical properties ofthe memory device are improved.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic cross-sectional view of a conventionalnon-volatile memory.

FIGS. 2A through 2C are schematic cross-sectional views showing thesteps for fabricating a non-volatile memory according to one preferredembodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a non-volatile memoryaccording to one preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIGS. 2A through 2C are schematic cross-sectional views showing thesteps for fabricating a non-volatile memory according to one embodimentof the present invention. As shown in FIG. 2A, a semiconductor substrate200 is provided. Next, a plurality of stack structures 212 is formedover the substrate 200. Each stack structure 212 comprises, from bottomto top, a bottom dielectric layer 214, a charge trapping layer 216, atop dielectric layer 218, a control gate 220 and a cap layer 210. Thestack structures 212 are formed, for example, by sequentially forming abottom dielectric layer 214, a charge-trapping material layer 216, a topdielectric material layer 218, a control gate layer 220 and a cap layer210 over the substrate 200 and patterning the aforementioned layers.Since the materials, the steps and other operating parameters related tothe fabrication of the stack structures should be familiar to the onesskilled in the art of semiconductor fabrication, a detailed descriptionis omitted here.

Thereafter, as shown in FIG. 2A, a plurality of spacers 222 is formed onthe respective sidewalls of each stack structure 212. The spacers 222are silicon nitride or silicon oxide layer formed, for example, bydepositing spacer material (not shown) over the semiconductor substrate200 to cover the stack structures 212 and then etching back the spacermaterial layer.

As shown in FIG. 2B, a gate dielectric layer 224 is formed over thesemiconductor substrate 200. The gate dielectric layer 224 is a siliconoxide layer formed, for example, by performing a thermal oxidationprocess. Thereafter, a conductive layer 226 is formed over thesemiconductor substrate 200 to cover the stack structures 212 and fillup the space between neighboring two stack structures 212. Theconductive layer 226 is a doped polysilicon layer formed by performing achemical vapor deposition (CVD) process, for example. After that, aportion of the conductive layer 226 is removed to expose the cap layer210 of various stack structures 212. The method of removing a portion ofthe conductive layer 226 includes performing a chemical-mechanicalpolishing operation using the cap layer 210 of various stack structures212 as a polishing stop layer. In another preferred embodiment, themethod of removing a portion of the conductive layer 226 to expose thecap layer 210 of various stack structures 212 includes etching back theconductive layer 226 using the cap layer 210 of various stack structures212 as an etching stop layer. Next, a patterned photoresist layer 228 isformed over the substrate 200 to cover the conductive layer 226 betweentwo stack structures 212 so that at least a portion of the cap layer 210is exposed.

As shown in FIG. 2C, the cap layer 210 of the stack structures 212 andthe conductive layer 226 not covered by the photoresist layer 228 areremoved. The method of removing the cap layer 210 and the exposedconductive layer 226 includes performing a wet etching operation usingthe photoresist layer 228 as a mask so that a word line 230 is formedbetween two neighboring stack structures 212.

Thereafter, as shown in FIG. 2C, the photoresist layer 228 is removedand then a source region 232 and a drain region 234 are formed in thesemiconductor substrate 200 beside the stack structures 212 on each sideof the word line 230. The method of forming the source region 232 andthe drain region 234 includes performing an ion implantation process,for example.

In the aforementioned method of forming the non-volatile memory, thespacers 222 between the control gate 220 and the word line 230 has abetter quality. Hence, in a subsequent process of forming a silicidelayer (not shown), short-circuiting phenomenon rarely occurs. In otherwords, the electrical properties of the non-volatile memory areimproved.

Since subsequent processes for producing a complete non-volatile memoryshould be familiar to everyone knowledgeable about memory fabrication, adetailed description of those steps is omitted.

In the following, the structure of a non-volatile memory fabricatedusing the aforementioned method is described with reference to FIG. 3.FIG. 3 is a schematic cross-sectional view of a non-volatile memoryaccording to one embodiment of the present invention. As shown in FIG.3, the non-volatile memory mainly comprises a semiconductor substrate300, a plurality of stack structures 312, a plurality of spacers 322, agate dielectric layer 324, a word line 330, a source region 332 and adrain region 334. The plurality of stack structures 312 is disposed onthe semiconductor substrate 300. Each stack structure 312 comprises abottom dielectric layer 314, a charge trapping layer 316, a topdielectric layer 318 and a control gate 320.

The bottom dielectric layer 314 is disposed on the semiconductorsubstrate 300. The bottom dielectric layer 314 is fabricated using anon-conductive material including silicon oxide, for example. Thecharge-trapping layer 316 is disposed on the bottom oxide layer 314. Thecharge-trapping layer 316 is fabricated using a non-conductive materialincluding silicon nitride, for example. The top dielectric layer 318 isdisposed on the charge-trapping layer 316. The top dielectric layer 318is fabricated using a non-conductive material including silicon oxide,for example. The control gate 320 is disposed on the top dielectriclayer 318 and has a planar surface, for example. The control gate 320 isfabricated using a conductive material including doped polysilicon, forexample.

Furthermore, the word line 330 is disposed on the semiconductorsubstrate 300 and located between two neighboring stack structures 312.The word line 330 is fabricated using doped polysilicon, for example.The spacers 322 are disposed between the stack structures 312 and theircorresponding word lines 330. The spacers 322 are fabricated using anon-conductive material including silicon nitride or silicon oxide, forexample. The gate dielectric layer 324 is disposed between the word line330 and the semiconductor substrate 300. The gate dielectric layer 324is fabricated using silicon oxide, for example. The source region 332and the drain region 334 are disposed in the semiconductor substrate 300beside the stack structures 312 on each side of the word line 330.

In the non-volatile memory of the present invention, there is nooxide-nitride-oxide structure on the sidewalls of the word lines 330 asin the conventional silicon-oxide-nitride-oxide-semiconductor (SONOS)memory structure. Hence, there is no need to worry about chargestrapping in the oxide-nitride-oxide structure next to the sidewalls ofthe word lines 330. In other words, overall reliability of the memorydevice is improved. In addition, the control gate 320 of thenon-volatile memory of the present invention has a planar top surfacewith a rectangular outline. Therefore, it is much easier to form anelectrical connection between the control gate 320 and a contact in asubsequent contact fabrication process.

In summary, the advantages of the present invention includes as follows.

1. The non-volatile memory in the present invention is able to resolvethe problem of electric charges trapped in the oxide-nitride-oxidestructure on the sidewalls of the word line in the conventionaltechnique. Hence, the overall reliability of the memory device isimproved.

2. The control gate has a planar top surface so that the process offorming an electrical connection between the control gate and a contactis very much facilitated.

3. The spacers between the word lines and the control gates have abetter quality so that the chance of short-circuiting after forming asilicide layer is reduced. Thus, the electrical properties of the memorydevice are improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A non-volatile memory, comprising: a substrate; a plurality of stackstructures disposed on the substrate with each stack structure having: abottom dielectric layer disposed on the substrate; a charge trappinglayer disposed on the bottom dielectric layer; a top dielectric layerdisposed on the charge trapping layer; and a control gate disposed onthe top dielectric layer; a plurality of word lines disposed on thesubstrate between every pair of neighboring stack structures; aplurality of spacers disposed between the stack structures and theircorresponding word lines; a gate dielectric layer disposed between theword lines and the substrate; and a plurality of source regions and aplurality of drain regions with each corresponding pair of source regionand drain region disposed in the substrate beside the stack structureson each side of the word line.
 2. The non-volatile memory of claim 1,wherein the control gate has a planar top surface.
 3. The non-volatilememory of claim 1, wherein the bottom dielectric layer and the topdielectric layer in the stack structure are fabricated using anon-conductive material.
 4. The non-volatile memory of claim 3, whereinthe non-conductive material comprises silicon oxide.
 5. The non-volatilememory of claim 1, wherein the charge trapping layer of the stackstructures is fabricated using a non-conductive material.
 6. Thenon-volatile memory of claim 5, wherein the non-conductive materialcomprises silicon nitride.
 7. The non-volatile memory of claim 1,wherein the spacers are fabricated using a non-conductive material. 8.The non-volatile memory of claim 7, wherein the non-conductive materialcomprises silicon nitride or silicon oxide.
 9. The non-volatile memoryof claim 1, wherein the word lines and the control gates are fabricatedusing a conductive material.
 10. The non-volatile memory of claim 9,wherein the conductive material comprises doped polysilicon.